The invention relates to a non-segregating, pumpable organic peroxide-containing aqueous suspension suitable for the (co)polymerization of ethylenically unsaturated monomers and to this suspension per se.
It is known that vinyl halides such as vinyl chloride; vinyl bromide; and vinyl fluoride can be polymerized or, in combination with vinylidene halides such as vinylidene chloride and vinylidene fluoride or in combination with other terminal CH.sub.2 = C &lt; groups containing compounds, such as ethylene, propylene and vinyl acetate, can be polymerized. This polymerization or copolymerization usually takes place in water. To this end, the monomer to be polymerized or the monomer mixture to be copolymerized is dispersed in water in the presence of a protective colloid or an emulsifier, followed by the addition of a compound yielding free radicals to initiate (co)polymerization. For this purpose, use may be made of at room temperature solid peroxydicarbonates such as dimyristyl peroxydicarbonate, dicetyl peroxydicarbonate, distearyl peroxydicarbonate, bis (4-tert. butylcyclohexyl) peroxydicarbonate, bis (4-tert. amylcyclohexyl) peroxydicarbonate, dicyclohexyl peroxydicarbonate and dibenzyl peroxydicarbonate. Said peroxides display storage stability at room temperature.
When for feeding purposes, however, these peroxy dicarbonates are dissolved in organic solvents such as acetone, benzene or chloroform, the chemical stability of these peroxy compounds very much decreases. Moreover, such solutions may give rise to strong reactions, spontaneous ignition and even explosions if no care is taken that the heat released upon decomposition is carried off.
U.S. Pat. Specification No. 3,825,509 describes a process for the suspension polymerization of vinyl chloride alone or in combination with vinylidene monomers copolymerizable therewith, in which process the initiator is an emulsion of an organic peroxide in an aqueous solution containing 1 - 10% by weight of polyvinyl alcohol and 1 - 6% by weight of polyoxyethylene sorbitan monolaurate.
This emulsion has the disadvantage that it must not contain more than about 19% by weight of organic peroxide, higher concentration leading to a too viscous emulsion which is, therefore, difficult to handle. The additional disadvantage to these emulsions is that it can only be prepared at temperatures in the range of 5.degree.- 10.degree. C. and must be stored at 0.degree. C. or even lower temperature.
U.S. Patent Specification No. 3,507,800 describes a flame resistant, pasty composition which mainly consists of water, an organic peroxide and a mutual solvent for the water and the organic peroxide. In the patent specification, a distinction is made between on the one hand peroxides derived from (cyclo) aliphatic ketones, such as methyl ethyl ketone peroxide, acetone peroxide, methyl amyl ketone peroxide, cyclopentanone peroxide, and on the other hand, benzoyl peroxide and chlorinated derivatives thereof such as 2,4-dichlorobenzoyl peroxide.
The former category is incorporated in the paste in an amount not higher than 30% by weight, benzoyl peroxide or the nuclear-chlorinated derivatives thereof, in an amount of not more than 50% by weight. As solvents for pastes containing the former category of organic peroxides are recommended liquid or water-soluble aliphatic polyoxyalkanes and alkyl esters. As solvents for benzoyl peroxide-containing pastes are mentioned compounds such as precipitated, finely divided silica, alkyl cellulose, etc., which compounds may form a gel with the water contained in the paste. Mention is also made of compounds known under the name of detergent. The compositions described in U.S. Pat. No. 3,507,800 have the disadvantage that they are pasty.
They are, therefore, less suitable to be used as catalyst in (co)polymerization reactions carried out in a closed system in order to prevent the escape of monomers, e.g., vinyl chloride, detrimental to health. In such techniques, the composition to be used should be pumpable.